Optical films are often use in combination with an optically diffusive layer (a “diffuser”); for example, to increase viewing angle. When typical diffusers are applied to the bottom of optical films they reduce gain. Diffusers are used in liquid crystal displays (LCDs) to hide the light bulbs used as backlights. Diffusers typically help make the light more uniform, but may reduce the transmission of light through the optical film, and/or reduce image clarity.
There are two main types of diffusers: surface diffusers wherein surface particles cause optical diffusion, and bulk diffusers wherein diffusive particles are dispersed throughout a binder. With surface diffusers, the particles typically have the same refractive index as the resin and the diffusion is limited to the air/bead interface (a single bounce). Typically, surface diffusers are oriented facing away from the light source in display constructions such as LCD displays. Bulk diffusers rely on having a difference in refractive index between the diffusive particle and the binder.